Isoprene is an important monomer for the production of specialty elastomers including motor mounts/fittings, surgical gloves, rubber bands, golf balls and shoes. Styrene-isoprene-styrene block copolymers form a key component of hot-melt pressure-sensitive adhesive formulations and cis-poly-isoprene is utilised in the manufacture of tires (Whited et al., Industrial Biotechnology, 2010, 6(3), 152-163). Manufacturers of rubber goods depend on either imported natural rubber from the Brazilian rubber tree or petroleum-based synthetic rubber polymers (Whited et al., Industrial Biotechnology, 2010, 6(3), 152-163).
1,3-Butadiene (referred to herein as “butadiene”) is an important monomer for the production of synthetic rubbers including styrene-butadiene-rubber (SBR), polybutadiene (PB), styrene-butadiene latex (SBL), acrylonitrile-butadiene-styrene resins (ABS), nitrile rubber, and adiponitrile. Adiponitrile is used in the manufacture of Nylon-6,6 (White, Chemico-Biological Interactions, 2007, 166, 10-14). Butadiene is typically produced as a co-product from the steam cracking process, distilled to a crude butadiene stream, and purified via extractive distillation (White, Chemico-Biological Interactions, 2007, 166, 10-14). On-purpose butadiene has been prepared among other methods by dehydrogenation of n-butane and n-butene (Houdry process); and oxidative dehydrogenation of n-butene (Oxo-D or O-X-D process) (White, Chemico-Biological Interactions, 2007, 166, 10-14). Industrially, 95% of global butadiene production is undertaken via the steam cracking process using petrochemical-based feedstocks such as naphtha. Production of on-purpose butadiene is not significant, given the high cost of production and low process yield (White, Chemico-Biological Interactions, 2007, 166, 10-14).
Isobutene is an important monomer in the manufacture of fuel additives, butyl rubber polymer, and antioxidants (Bianca et al., Appl. Microbiol Biotechnol., 2012, 93, 1377-1387). Manufacturers of goods using isobutene as feedstock depend on a number of petroleum-based sources, including (i) a C4 stream from a steam cracker separated from the butadiene, (ii) butene-butane fractions from a catalytic cracker and (iii) n-butane (from LPG) that is isomerized to isobutane and dehydrogenated to isobutene (Bianca et al., Appl. Microbiol Biotechnol., 2012, 93, 1377-1387).
Given a reliance on petrochemical feedstocks, biotechnology offers an alternative approach to producing alkene precursors to isoprene, butadiene and isobutene. Biocatalysis is the use of biological catalysts, such as enzymes or whole cells, to perform biochemical transformations of organic compounds.
Accordingly, against this background, it is clear that there is a need for sustainable methods for producing precursors to commodity alkenes, in particular isoprene, isobutene and butadiene, wherein the precursors are biocatalysis based.